import os
import arrow

from gitlint import shell as sh
# import exceptions separately, this makes it a little easier to mock them out in the unit tests
from gitlint.shell import CommandNotFound, ErrorReturnCode

from gitlint.cache import PropertyCache, cache
from gitlint.utils import ustr, sstr

# For now, the git date format we use is fixed, but technically this format is determined by `git config log.date`
# We should fix this at some point :-)
GIT_TIMEFORMAT = "YYYY-MM-DD HH:mm:ss Z"


class GitContextError(Exception):
    """ Exception indicating there is an issue with the git context """
    pass


class GitNotInstalledError(GitContextError):
    def __init__(self):
        super(GitNotInstalledError, self).__init__(
            u"'git' command not found. You need to install git to use gitlint on a local repository. " +
            u"See https://git-scm.com/book/en/v2/Getting-Started-Installing-Git on how to install git.")


def _git(*command_parts, **kwargs):
    """ Convenience function for running git commands. Automatically deals with exceptions and unicode. """
    git_kwargs = {'_tty_out': False}
    git_kwargs.update(kwargs)
    try:
        result = sh.git(*command_parts, **git_kwargs)  # pylint: disable=unexpected-keyword-arg
        # If we reach this point and the result has an exit_code that is larger than 0, this means that we didn't
        # get an exception (which is the default sh behavior for non-zero exit codes) and so the user is expecting
        # a non-zero exit code -> just return the entire result
        if hasattr(result, 'exit_code') and result.exit_code > 0:
            return result
        return ustr(result)
    except CommandNotFound:
        raise GitNotInstalledError()
    except ErrorReturnCode as e:  # Something went wrong while executing the git command
        error_msg = e.stderr.strip()
        error_msg_lower = error_msg.lower()
        if '_cwd' in git_kwargs and b"not a git repository" in error_msg_lower:
            error_msg = u"{0} is not a git repository.".format(git_kwargs['_cwd'])
        elif (b"does not have any commits yet" in error_msg_lower or
              b"ambiguous argument 'head': unknown revision" in error_msg_lower):
            raise GitContextError(u"Current branch has no commits. Gitlint requires at least one commit to function.")
        else:
            error_msg = u"An error occurred while executing '{0}': {1}".format(e.full_cmd, error_msg)
        raise GitContextError(error_msg)


def git_version():
    """ Determine the git version installed on this host by calling git --version"""
    return _git("--version").replace(u"\n", u"")


def git_commentchar(repository_path=None):
    """ Shortcut for retrieving comment char from git config """
    commentchar = _git("config", "--get", "core.commentchar", _cwd=repository_path, _ok_code=[0, 1])
    # git will return an exit code of 1 if it can't find a config value, in this case we fall-back to # as commentchar
    if hasattr(commentchar, 'exit_code') and commentchar.exit_code == 1:  # pylint: disable=no-member
        commentchar = "#"
    return ustr(commentchar).replace(u"\n", u"")


def git_hooks_dir(repository_path):
    """ Determine hooks directory for a given target dir """
    hooks_dir = _git("rev-parse", "--git-path", "hooks", _cwd=repository_path)
    hooks_dir = ustr(hooks_dir).replace(u"\n", u"")
    return os.path.realpath(os.path.join(repository_path, hooks_dir))


class GitCommitMessage(object):
    """ Class representing a git commit message. A commit message consists of the following:
      - context: The `GitContext` this commit message is part of
      - original: The actual commit message as returned by `git log`
      - full: original, but stripped of any comments
      - title: the first line of full
      - body: all lines following the title
    """
    def __init__(self, context, original=None, full=None, title=None, body=None):
        self.context = context
        self.original = original
        self.full = full
        self.title = title
        self.body = body

    @staticmethod
    def from_full_message(context, commit_msg_str):
        """  Parses a full git commit message by parsing a given string into the different parts of a commit message """
        all_lines = commit_msg_str.splitlines()
        cutline = u"{0} ------------------------ >8 ------------------------".format(context.commentchar)
        try:
            cutline_index = all_lines.index(cutline)
        except ValueError:
            cutline_index = None
        lines = [ustr(line) for line in all_lines[:cutline_index] if not line.startswith(context.commentchar)]
        full = "\n".join(lines)
        title = lines[0] if lines else ""
        body = lines[1:] if len(lines) > 1 else []
        return GitCommitMessage(context=context, original=commit_msg_str, full=full, title=title, body=body)

    def __unicode__(self):
        return self.full  # pragma: no cover

    def __str__(self):
        return sstr(self.__unicode__())  # pragma: no cover

    def __repr__(self):
        return self.__str__()  # pragma: no cover

    def __eq__(self, other):
        return (isinstance(other, GitCommitMessage) and self.original == other.original
                and self.full == other.full and self.title == other.title and self.body == other.body)  # noqa

    def __ne__(self, other):
        return not self.__eq__(other)  # required for py2


class GitCommit(object):
    """ Class representing a git commit.
        A commit consists of: context, message, author name, author email, date, list of parent commit shas,
        list of changed files, list of branch names.
        In the context of gitlint, only the git context and commit message are required.
    """

    def __init__(self, context, message, sha=None, date=None, author_name=None,  # pylint: disable=too-many-arguments
                 author_email=None, parents=None, changed_files=None, branches=None):
        self.context = context
        self.message = message
        self.sha = sha
        self.date = date
        self.author_name = author_name
        self.author_email = author_email
        self.parents = parents or []  # parent commit hashes
        self.changed_files = changed_files or []
        self.branches = branches or []

    @property
    def is_merge_commit(self):
        return self.message.title.startswith(u"Merge")

    @property
    def is_fixup_commit(self):
        return self.message.title.startswith(u"fixup!")

    @property
    def is_squash_commit(self):
        return self.message.title.startswith(u"squash!")

    @property
    def is_revert_commit(self):
        return self.message.title.startswith(u"Revert")

    def __unicode__(self):
        format_str = (u"--- Commit Message ----\n%s\n"
                      u"--- Meta info ---------\n"
                      u"Author: %s <%s>\nDate:   %s\n"
                      u"is-merge-commit:  %s\nis-fixup-commit:  %s\n"
                      u"is-squash-commit: %s\nis-revert-commit: %s\n"
                      u"Branches: %s\n"
                      u"Changed Files: %s\n"
                      u"-----------------------")  # pragma: no cover
        date_str = arrow.get(self.date).format(GIT_TIMEFORMAT) if self.date else None
        return format_str % (ustr(self.message), self.author_name, self.author_email, date_str,
                             self.is_merge_commit, self.is_fixup_commit, self.is_squash_commit,
                             self.is_revert_commit, sstr(self.branches), sstr(self.changed_files))  # pragma: no cover

    def __str__(self):
        return sstr(self.__unicode__())  # pragma: no cover

    def __repr__(self):
        return self.__str__()  # pragma: no cover

    def __eq__(self, other):
        # skip checking the context as context refers back to this obj, this will trigger a cyclic dependency
        return (isinstance(other, GitCommit) and self.message == other.message
                and self.sha == other.sha and self.author_name == other.author_name
                and self.author_email == other.author_email
                and self.date == other.date and self.parents == other.parents
                and self.is_merge_commit == other.is_merge_commit and self.is_fixup_commit == other.is_fixup_commit
                and self.is_squash_commit == other.is_squash_commit and self.is_revert_commit == other.is_revert_commit
                and self.changed_files == other.changed_files and self.branches == other.branches) # noqa

    def __ne__(self, other):
        return not self.__eq__(other)  # required for py2


class LocalGitCommit(GitCommit, PropertyCache):
    """ Class representing a git commit that exists in the local git repository.
        This class uses lazy loading: it defers reading information from the local git repository until the associated
        property is accessed for the first time. Properties are then cached for subsequent access.

        This approach ensures that we don't do 'expensive' git calls when certain properties are not actually used.
        In addition, reading the required info when it's needed rather than up front avoids adding delay during gitlint
        startup time and reduces gitlint's memory footprint.
     """
    def __init__(self, context, sha):  # pylint: disable=super-init-not-called
        PropertyCache.__init__(self)
        self.context = context
        self.sha = sha

    def _log(self):
        """ Does a call to `git log` to determine a bunch of information about the commit. """
        long_format = "--pretty=%aN%x00%aE%x00%ai%x00%P%n%B"
        raw_commit = _git("log", self.sha, "-1", long_format, _cwd=self.context.repository_path).split("\n")

        (name, email, date, parents), commit_msg = raw_commit[0].split('\x00'), "\n".join(raw_commit[1:])

        commit_parents = parents.split(" ")
        commit_is_merge_commit = len(commit_parents) > 1

        # "YYYY-MM-DD HH:mm:ss Z" -> ISO 8601-like format
        # Use arrow for datetime parsing, because apparently python is quirky around ISO-8601 dates:
        # http://stackoverflow.com/a/30696682/381010
        commit_date = arrow.get(ustr(date), GIT_TIMEFORMAT).datetime

        # Create Git commit object with the retrieved info
        commit_msg_obj = GitCommitMessage.from_full_message(self.context, commit_msg)

        self._cache.update({'message': commit_msg_obj, 'author_name': name, 'author_email': email, 'date': commit_date,
                            'parents': commit_parents, 'is_merge_commit': commit_is_merge_commit})

    @property
    def message(self):
        return self._try_cache("message", self._log)

    @property
    def author_name(self):
        return self._try_cache("author_name", self._log)

    @property
    def author_email(self):
        return self._try_cache("author_email", self._log)

    @property
    def date(self):
        return self._try_cache("date", self._log)

    @property
    def parents(self):
        return self._try_cache("parents", self._log)

    @property
    def branches(self):
        def cache_branches():
            # We have to parse 'git branch --contains <sha>' instead of 'git for-each-ref' to be compatible with
            # git versions < 2.7.0
            # https://stackoverflow.com/questions/45173979/can-i-force-git-branch-contains-tag-to-not-print-the-asterisk
            branches = _git("branch", "--contains", self.sha, _cwd=self.context.repository_path).split("\n")

            # This means that we need to remove any leading * that indicates the current branch. Note that we can
            # safely do this since git branches cannot contain '*' anywhere, so if we find an '*' we know it's output
            # from the git CLI and not part of the branch name. See https://git-scm.com/docs/git-check-ref-format
            # We also drop the last empty line from the output.
            self._cache['branches'] = [ustr(branch.replace("*", "").strip()) for branch in branches[:-1]]

        return self._try_cache("branches", cache_branches)

    @property
    def is_merge_commit(self):
        return self._try_cache("is_merge_commit", self._log)

    @property
    def changed_files(self):
        def cache_changed_files():
            self._cache['changed_files'] = _git("diff-tree", "--no-commit-id", "--name-only", "-r", "--root",
                                                self.sha, _cwd=self.context.repository_path).split()

        return self._try_cache("changed_files", cache_changed_files)


class StagedLocalGitCommit(GitCommit, PropertyCache):
    """ Class representing a git commit that has been staged, but not committed.

        Other than the commit message itself (and changed files), a lot of information is actually not known at staging
        time, since the commit hasn't happened yet. However, we can make educated guesses based on existing repository
        information.
    """

    def __init__(self, context, commit_message):  # pylint: disable=super-init-not-called
        PropertyCache.__init__(self)
        self.context = context
        self.message = commit_message
        self.sha = None
        self.parents = []  # Not really possible to determine before a commit

    @property
    @cache
    def author_name(self):
        return ustr(_git("config", "--get", "user.name", _cwd=self.context.repository_path)).strip()

    @property
    @cache
    def author_email(self):
        return ustr(_git("config", "--get", "user.email", _cwd=self.context.repository_path)).strip()

    @property
    @cache
    def date(self):
        # We don't know the actual commit date yet, but we make a pragmatic trade-off here by providing the current date
        # We get current date from arrow, reformat in git date format, then re-interpret it as a date.
        # This ensure we capture the same precision and timezone information that git does.
        return arrow.get(arrow.now().format(GIT_TIMEFORMAT), GIT_TIMEFORMAT).datetime

    @property
    @cache
    def branches(self):
        # We don't know the branch this commit will be part of yet, but we're pragmatic here and just return the
        # current branch, as for all intents and purposes, this will be what the user is looking for.
        return [self.context.current_branch]

    @property
    def changed_files(self):
        return _git("diff", "--staged", "--name-only", "-r", _cwd=self.context.repository_path).split()


class GitContext(PropertyCache):
    """ Class representing the git context in which gitlint is operating: a data object storing information about
    the git repository that gitlint is linting.
    """

    def __init__(self, repository_path=None):
        PropertyCache.__init__(self)
        self.commits = []
        self.repository_path = repository_path

    @property
    @cache
    def commentchar(self):
        return git_commentchar(self.repository_path)

    @property
    @cache
    def current_branch(self):
        current_branch = ustr(_git("rev-parse", "--abbrev-ref", "HEAD", _cwd=self.repository_path)).strip()
        return current_branch

    @staticmethod
    def from_commit_msg(commit_msg_str):
        """ Determines git context based on a commit message.
        :param commit_msg_str: Full git commit message.
        """
        context = GitContext()
        commit_msg_obj = GitCommitMessage.from_full_message(context, commit_msg_str)
        commit = GitCommit(context, commit_msg_obj)
        context.commits.append(commit)
        return context

    @staticmethod
    def from_staged_commit(commit_msg_str, repository_path):
        """ Determines git context based on a commit message that is a staged commit for a local git repository.
        :param commit_msg_str: Full git commit message.
        :param repository_path: Path to the git repository to retrieve the context from
        """
        context = GitContext(repository_path=repository_path)
        commit_msg_obj = GitCommitMessage.from_full_message(context, commit_msg_str)
        commit = StagedLocalGitCommit(context, commit_msg_obj)
        context.commits.append(commit)
        return context

    @staticmethod
    def from_local_repository(repository_path, refspec=None):
        """ Retrieves the git context from a local git repository.
        :param repository_path: Path to the git repository to retrieve the context from
        :param refspec: The commit(s) to retrieve
        """

        context = GitContext(repository_path=repository_path)

        # If no refspec is defined, fallback to the last commit on the current branch
        if refspec is None:
            # We tried many things here e.g.: defaulting to e.g. HEAD or HEAD^... (incl. dealing with
            # repos that only have a single commit - HEAD^... doesn't work there), but then we still get into
            # problems with e.g. merge commits. Easiest solution is just taking the SHA from `git log -1`.
            sha_list = [_git("log", "-1", "--pretty=%H", _cwd=repository_path).replace(u"\n", u"")]
        else:
            sha_list = _git("rev-list", refspec, _cwd=repository_path).split()

        for sha in sha_list:
            commit = LocalGitCommit(context, sha)
            context.commits.append(commit)

        return context

    def __eq__(self, other):
        return (isinstance(other, GitContext) and self.commits == other.commits
                and self.repository_path == other.repository_path
                and self.commentchar == other.commentchar and self.current_branch == other.current_branch)  # noqa

    def __ne__(self, other):
        return not self.__eq__(other)  # required for py2